Conventional mobile communications scheme like the W-CDMA (wideband-Code Division Multiple Access) defined by 3GPP (3rd Generation Partnership Project) only standardize implementations in which base stations (called NodeB in 3GPP) are directly connected to a base station controller (called RNC (radio Network Controller) in 3GPP)(See Non-patent Document 1).
Also, in general, considering the configuration of the base station controller, the number of base stations already used in service change software, or change hardware by providing additional memory, for example.
In contrast to the 3GPP, in connections between mobile communications networks such as PHS (personal Handyphone System) and public networks, there are techniques that use base station concentrators as higher-level devices that supervise the base stations. When such a base station concentrator is connected to a plurality of base stations to make connections with the base stations and public network, the base station concentrator supplies a frame synchronization signal to the base stations so that frame synchronization can be established among the plurality of base stations on the basis of the frame synchronization signal from the base station concentrator. (For example, see Patent Document 1.)    Non-patent Document 1: 3GPP TS (Technical Specification) 25.401 V3.10.0, 2002-06, retrieved from the Internet [retrieved on 2005-01-24]: <URL: http://www.3gpp.org/ftp/Specs/latest/R1999/25_series/25401-3a0.zip>.    Patent Document 1: Japanese Patent Application Laid-Open No. 2002-094441    Patent Document 2: Japanese Patent Application Laid-Open No. 08-237731 (1996)